The present invention relates to a through hole connector which provides electrical communication between wiring patterns formed on two opposing major surfaces of an insulator circuit board.
In the conventional circuit board which carries wiring patterns formed on its two opposing major surfaces, through holes are formed at desired positions after conductive layers are formed on the entire surface of the opposing major surfaces of the circuit board. Inner surfaces of the thus formed through holes are coated with plated layers through the use of a chemical plating method or a chemical/electrical plating method, thereby providing electrical communication between the conductive layers formed on the two major surfaces with each other via the plated layers.
The through holes are formed through the use of a drilling method or a punching method. Therefore, there is the possibility that the circuit board or the conductive layers become distorted during the formation of the through holes. The thus formed distortion will adversely influence the formation of the plated layers so that an effective electrical connection can not be achieved between the two conductive layers. In addition, fine wiring patterns can not be formed near the through holes due to the distortion of the conductive layers.
Thereafter, the conductive layers are shaped in a desired configuration to obtain wiring patterns formed on both of the major surfaces of the circuit board. In the conventional system, a liquid photo-resist can not be employed because of the through holes formed in the circuit board. That is, the wiring patterns are formed, in the conventional system, through the use of a dry film or a resist sheet. Accordingly, fine wiring patterns can not be obtained because a minimum requirement in the thickness of the resist sheet.
Another example of prior art through hole connectors is disclosed in U.S. Pat. No. 3,601,523 "THROUGH HOLE CONNECTORS" by Lloyd G. Arndt, issued on Aug. 24, 1971, wherein a conductive adhesive is disposed in the through holes for providing electrical communication between the conductive layers formed on both of the major surfaces of the circuit board. In the device of U.S. Pat. No. 3,601,523, the through holes are formed after the conductive layers are formed on both of the major surfaces of the circuit board and, therefore, there is a possibility that the conductive layers will become distorted near the through holes. Moreover, in U.S. Pat. No. 3,601,523, electrical communication between the conductive layer and the conductive adhesive is achieved only through the use of the thickness of the conductive layer. In addition, the conductive adhesive is exposed to the ambience. Therefore, the shaping of the wiring patterns must be conducted through the use of a dry film or a resist sheet.